Ancovenin1), muraceins2), L-681,1763), 15B24) and phenacein5> which inhibit an angiotensinconverting enzyme have been found in culture broths of actinomycetes. Moreover, aspergillomarasmines6), products of fungi have also been reported to inhibit this enzyme. Testing the activity of culture filtrates of freshly isolated actinomycetes strains in inhibiting an angiotensin-converting enzyme (ACE, dipeptidyl carboxypeptidase EC 3.4.15.1), we found a new peptide and we named this inhibitor foroxymithine. The strain MG329-CF56 producing foroxymithine was found to belong to Streptomyces nitrosporeus. In this paper, the isolation, physico-chemical properties and biological activities of foroxymithine are reported. The structure of foroxymithine was determined and is shown in Fig. 1. The structural studies will soon be reported elsewhere.